ArcBruTile getting timeout: Full Internet access required?

one of our customers is using ArcGIS 10.0 and we told them to install ArcBruTile 0.3.3. Our evaulation installation (ArcGIS 10.1) works fine with it, but our customer has big problems.

They try to add a TMS Service by clicking in the toolbar "ArcBruTile"--->"Add TMS Service" and it opens a dialog window, where they can add new TMS Provider. When clicking "Add provider", nothing happens for a long
time and it seems that ArcGIS crashed.

I could imagine, that this is because they are in a firewalled network where they have access to dns-servers so they can resolve dns names and access network-local services but not the internet.